Isostructural Halogen Exchange and Halogen Bonds: The Case of N-(4-Halogenobenzyl)-3-halogenopyridinium Halogenides

Abstract

Six N -(4-halogenobenzyl)-3-halogenopyridinium cations were prepared by reacting meta -halogenopyridines (Cl, Br, and I) with (4-halogenobenzyl) bromides (Br and I) and were isolated as bromide salts, which were further used to obtain iodides and chlorides. Sixteen compounds (out of 18 possible cation/anion combinations) were obtained; two crystallized as hydrates and 14 as solvent free salts, 11 of which belonged to one isostructural series and 3 to another. All crystal structures comprise halogen-bonded chains, with the anion as an acceptor of two halogen bonds, with the pyridine and the benzyl halogen substituents of two neighboring cations. The halogen bonds with the pyridine halogen show a linear correlation between the relative halogen bond length and angle, which primarily depend on the donor halogen. The parameters of the other halogen bonds vary with all three halogens, indicating that the former halogen bond is the dominant interaction. This is also in accord with the calculated electrostatic potential in the σ-holes of the halogens and the thermal properties of the solids. The second isostructural group comprises combinations of the best halogen bond donors and acceptors, and features a more favorable halogen bond geometry of the dominant halogen bond, reaffirming its significance as the main factor in determining the structure.

Crystal structures of 5-bromo-1-arylpyrazoles and their halogen bonding features

“…In the case of EJULON the distance is 96% of the sum of the vdW radii compared to 5 which is at the limit of the sum of the vdW radii. We can deduce from both examples that the two structures EJULON and compound 5 are isostructural 63,64 in that they crystallize in the same space group Pbca with isostructural molecular and crystal packing arrangements, as well as corresponding fingerprint plots.…”

Halogen-Bonded Mono-, Di-, and Tritopic N-Alkyl-3-iodopyridinium Salts

“…Above examples along with the data in the Cambridge Structural Database (CSD, total 251 hits) including very recent studies by Stilinović and co-workers − show that the cationic 3IPy + unit is more common and usually a stronger halogen bond donor than the neutral 3IPy moiety. However, halogen bonds in 3IPy + systems can be considered secondary interactions due to the strong attractive ionic forces dominating the crystal packing.…”

Cocrystals assembled from iodoperfluorobenzene and flexible NTPO via halogen and π-hole bonds

“…In order to meet this challenge, it is necessary to have an in-depth understanding of the noncovalent interactions responsible for the specific crystalline arrangements and the predictable physical/chemical properties. Among them, �-hole bonds (especially for halogen bonds) and �-hole bonds, as fashionable noncovalent interactions (Wang et al, 2016), have attracted increasing attention because of their promising applications in the realm of crystal engineering (Fotovic ´et al, 2022;Hasija & Chopra, 2020;Ji et al, 2021), materials chemistry (Ball et al, 2022;Bhowal et al, 2019;Kampes et al, 2021;, molecular recognition (Borissov et al, 2019;Molina et al, 2017;Pancholi & Beer, 2020; and catalysis (Kaasik & Kanger, 2020;Luo et al, 2022;Sutar & Huber, 2019;Zhao et al, 2018).…”